Consideration Of Strain Rate Effect Research Articles

Study on the energy transfer efficiency of explosive blasting with different coupling medium

Decoupled charge blasting can effectively reduce the peak pressure of hole wall and improve the blasting effect. Aiming at the issues associated with the explosive energy transferred into rock mass with different coupling medium, the deformation and failure characteristics of rock mass under explosion were analyzed theoretically with the consideration of strain rate effect of the rock mass, and the theoretical energy transfer efficiency of blasting with different coupling medium was obtained. Combined with the numerical simulations, the effects of rock mass properties, explosive categories and decoupled charge coefficient on the energy transfer efficiency of blasting with different coupling medium were studied. The results show that the energy transferred into rock mass from explosive of decoupling charge blasting is related to the coupling medium, the energy transfer efficiency of water coupling blasting is higher than that of air coupling blasting for the same charge structure and same blasting medium. When the charge structure and blasting rock mass are the same but the coupling medium is different, the energy transferred into the rock mass from explosive will be different, depending on blasting rock mass, explosive categories and decoupling charge coefficient. When blasting with the same decoupling charge coefficient but different coupling medium, the higher the rock mass strength, the greater the difference of energy transfer efficiency between different coupling medium. For blasting with the same rock mass properties and same charge structure, the difference of energy transfer efficiency between air coupling blasting and water coupling blasting increases with the increase of decoupling charge coefficient. For emulsion explosive exploding in siltstone, when the decoupling charge coefficient increases from 1.28 to 3.44, the energy transferred from water coupling blasting to surrounding rock mass increases from 1.45 to 6.52 times of air coupling blasting. The research results are of great reference significance for optimizing blasting design, improving explosion energy distribution and increasing the explosion energy utilization rate.

Peridynamic modelling of blasting induced rock fractures

This paper presents a peridynamics-based computational approach for modelling blasting induced rock fractures. A new non-ordinary state-based peridynamics approach is proposed in conjunction with a Johnson-Holmquist (JH2) constitutive model to consider the pressure dependency, strain rate effect, and viscoplasticity of rocks under blasting loads. The fracturing process in a rock is assessed based on both the JH2 damage model and a tension failure model. The former evaluates the material response pertaining to excessive plastic strain and the latter is used to gauge failure based on tensile stress in consideration of strain rate effect. Detonation in the explosives is simulated using updated Lagrangian peridynamics in conjunction with Jones-Wilkins-Lee (JWL) equation of state. Simulations of single-hole blasting in granite rock are presented and compared with experimental records. The proposed approach is shown to capture reasonably well the plastic material failure surrounding the borehole as well as the tensile cracks on both radial and circumferential directions. Further sensitivity studies indicate that the intact strength parameters in the JH2 model and the tensile strength of material play a vital role in producing the obtained fracture patterns and should hereby be selected with care. The presented computational approach offers a rigorous basis for future development of versatile, multi-physics-integrated computational framework on rock blasting simulations.

A comparison study on the impact failure behavior of laminate and woven composites with consideration of strain rate effect and impact attitude

The anisotropy and heterogeneity of carbon fiber–reinforced polymer (CFRP) composites contribute to their complex failure characteristics, posing challenges for predicting their impact failure behavior. In this study, high-fidelity finite element models are established to predict the performance of laminated and woven composite panels impacted by a metallic projectile, with consideration of strain-rate effect and impact attitudes. The numerical models are experimentally validated and are applied to investigate the impact resistance of both composites under various impact conditions. The results indicate that the maximum ratio of delamination of laminated panel is about 0.4, which is greater than 0.2 of the woven panel. Woven panels can better withstand impact damage, while laminates are more prone to delamination under high-speed impacts loads.

Effect of Strain Rate on Impact Behavior of Aluminum Foam

Due to increase of terrorist threats and attacks, reasonable and economical designs for impact resistant protective structures are necessary. To ensure the appropriate use of aluminum foam panels as sacrificial panels, the compressive behavior of aluminum foam must be investigated. This work presents broad experimental and numerical investigations of the strain rate sensitivity of closed-cell aluminum foam and its effect on the strength parameters of foam. Air gun tests for direct impact testing and split Hopkinson pressure bar (SHPB) tests were performed to investigate the deformation and energy absorption characteristics of aluminum foam with an increase in strain rate. Along with these experiments, numerical finite element analyses for both air gun and SHPB tests were performed with LS-DYNA. For the explicit analysis, the strain rate was considered in the material model, and the experimental work was verified by the numerical approach. The deformations and yield strengths of the aluminum foam were investigated with increasing strain rate. Parametric analyses were also conducted to determine the minimum required thickness of aluminum foam and an equation is proposed to calculate the minimum foam thickness while considering the effect of the strain rate. Moreover, to ensure realistic and economical designs for protective structures, a recommendation was provided for the aluminum foam thickness. This concept is compared with another study where strain rate effect was not considered for a close range blast load resistant protective structure. The pressure transmitted through the aluminum foam to the attached concrete wall was measured and the magnitude of reflected and mitigated transmitted pressure was observed. Consideration of strain rate effect leads to a lower required foam thickness and a lower magnitude of the pressure transmitted to the structure.

A new constitutive model for steel fibre reinforced concrete subjected to dynamic loads

The use of steel fibre reinforced concrete (SFRC) in protective structures has gained worldwide interest due to its superior mechanical characteristics. At present, hydrocode material models have been frequently used to simulate the dynamic behaviour of SFRC subjected to impact and blast loads. However, as these material models are developed for normal concrete, much effort is required for model calibration, and their other drawbacks, such as the neglect of shear dilation and the inappropriate consideration of strain-rate effect, may lead to inaccuracies in numerical predictions. In this study, a new constitutive material model is developed for SFRC, in which the damage evolution, shear dilation and strain-rate dependent material properties are properly taken into account. The new material model could accurately capture the mechanical behaviours of SFRC (i.e. strain hardening and softening in both compression and tension) with simple input parameters. It is then incorporated into the commercial finite element code LS-DYNA to simulate the structural behaviour of SFRC components under various loading conditions. The effectiveness and accuracy of the new material model are validated against the reported experimental results.

Strain-rate effect on the compressive strength of brittle materials and its implementation into material strength model

This paper studies the strain-rate effect on the compressive strength of brittle materials and its implementation into a material strength model. It shows that most of the current practices to consider strain-rate effect on the compressive strength of brittle materials using uniaxial stress data and loading path are questionable. It demonstrates that the rapid increase of the dynamic compressive strength between the transition strain-rate and the upper limit strain-rate in a SHPB test is correlated with the change of stress state in SHPB specimen, i.e. the stress state in SHPB specimen is changed from uniaxial stress state toward uniaxial strain state with the continuous increase of strain-rate from the transition strain-rate. Dynamic increase factor (DIF) based on experimental data under uniaxial strain state is recommended for the consideration of strain-rate effect on the compressive strength of brittle materials. An associated method to implement the uniaxial strain DIF into material strength model is also proposed and verified. Discussion on the DIF formulae and their implementations in several popular strength models of concrete-like materials is presented.

Recommended Finite Element Formulations for the Analysis of Offshore Blast Walls in an Explosion

Abstract This study suggests relevant finite element (FE) formulations for the structural analysis of offshore blast walls subjected to blast loadings due to hydrocarbon explosions. The present blast wall model adopted from HSE (2003) consists of a corrugated panel and supporting members, and was modelled with shell, thick-shell, and solid element combinations in LS-DYNA, an explicit finite element analysis (FEA) solver. Stainless and mild steels were employed as materials for the blast wall model, with consideration of strain rate effect throughout ten (10) pulse pressure load regimes. The obtained FEA results were validated by experimental data from HSE (2003) with decent agreement. In the present study, recommended FE formulations with additional hourglass control functions were widely discussed from the perspectives of solution accuracy and computational cost based on a statistical approach. The obtained outcomes could be used for the structural analysis and design of offshore blast walls in the estimations of maximum and permanent deformations under blast loadings.

Effects of temperature and strain rate on mechanical behavior of low-silver lead-free solder under drop impact

This study uses finite element program to simulate the process of board-level drop for portable electronic devices, so as to create very-thin-profile fine-pitch BGA packages model. Based on the data from quasi-static tests and the experimental data measured by split Hopkinson pressure bar, the parameters of Cowper–Symonds model about solder joints were obtained, taking into consideration of strain rate effect and temperature effect. The results show that, the maximum stress in Cowper–Symonds material model considering strain rate effect is significantly lower than that in linear elastic material model, and the location of maximum stress is different. When the temperature is −45, 23 or 60 °C, low silver lead-free solder Sn0.3Ag0.7Cu shows temperature softening effect obviously. Under low temperature, stress is concentrated at the interface of solder, while under normal temperature or high temperature the phenomenon is different obviously. Additionally, compared with high silver solder, low silver solder has better resistance to drop at room temperature or under working conditions.

ひずみ速度依存性を考慮した薄肉円筒の軸方向衝突における第一ピーク荷重

ひずみ速度依存性を考慮した薄肉円筒の軸方向衝突における第一ピーク荷重

Continuous velocity fields for the T‐bar problem

AbstractThis paper deals with the problem of T‐bar penetration. New kinematically admissible velocity fields are derived from elastic solutions of incompressible material using Airy stress function. These velocity fields are used to obtain upper bounds to collapse loads. Two particular solutions are presented, one for a rough contact surface between the T‐bar and soil and the other for a smooth contact surface. The merit of the solutions is that within the boundaries of the velocity field, the soil is required to shear compatibly and continuously. Therefore, these solutions can easily be combined with the strain path method to estimate rate and softening effects. Analysis including consideration of strain rate effect showed that the new mechanisms predict, under certain conditions, lower values than previously published upper bound solutions. Copyright © 2007 John Wiley & Sons, Ltd.

衝突条件が異なる衝撃力を受ける鉄筋コンクリートはりの有限要素法による挙動解析

The application method concerning the analysis of behavior of reinforced concrete beam using finite element method was investigated through comparison with experiment results. At first, it was confirmed that static behaviors reinforced concrete beam could be well reproduced using the Drucker-Prager model for concrete and the bilinear model for reinforcing steel bar having taken into consideration of strain rate effect. Finally it was also shown that the impact behaviors of reinforced concrete beam with a rubber as shock absorbing material on a collision part could be well represented by using the Arruda-Boyce model.